The present invention relates to a goniometer in an X-ray diffraction device, and more particularly to an improvement of a goniometer which is used in conjunction with an X-ray diffraction device, such as a diffractometer.
An X-ray diffraction device, such as a diffractometer, has been used for X-ray diffraction analysis. In X-ray diffraction analysis by the diffractometer, a crystal structure of a substance, for example, is analyzed by irradiating an X-ray onto the substance and measuring a diffraction angle of the X-ray reflected from or passed through the substance. A goniometer is employed in conjunction with the diffractometer for measuring a diffraction angle of the X-ray.
Next, a basic structure of a conventional goniometer will be described with reference to FIG. 12.
The goniometer comprises an X-ray source 60, a receiving slit 61, X-ray detector 62, and a sample table for holding a sample 63. The X-ray source 60 and the receiving slit 61 are disposed so that the distance L1 between the X-ray source 60 and the sample 63 is equal to the distance L2 between the receiving slit 61 and the sample 63. Therefore, the X-ray source 60 and the receiving slit 61 are always positioned on a predetermined circle 64 having a radius of L1 (=L2) which is drawn around a center axis 0 of the sample 63. The predetermined circle 64 is referred to as the diffractometer circle. The goniometer is classified into two types depending upon the plane in which its diffractometer circle is included, one of which is of a lateral type having the diffractometer circle in a horizontal plane, the other of which is of a vertical type having the diffractometer circle in a vertical plane.
In the goniometer, in order to change an incident angle (.theta.) of the X-ray with respect to a lattice plane of a sample, it is necessary to change a relative position between the X-ray source 60 and the sample 63. In accordance with the change of the relative position therebetween, it is further necessary to change a relative position between the receiving slit 61 and the sample 63 so that the diffracted X-ray is received in the receiving slit 61. Accordingly, in the conventional goniometer, two selected arbitarily from the X-ray source 60, the sample 63 and the receiving slit 61 are made to be rotatable about the center axis 0 of the sample 63 while unrotatably fixing the remainder. Depending upon the component unrotatably fixed, the goniometer is classified into three types; the X-ray source fixed type (referred to as .theta.-2.theta. operation system) in which the X-ray source is unrotatably fixed, the sample table fixed type (referred to as .theta.--.theta. operation system) and the receiving slit fixed type (or the X-ray detector fixed type). These three types of goniometers are applicable to both the lateral and vertical types of goniometers aforementioned. In general, employed are the X-ray source fixed and the lateral type goniometer, the X-ray source fixed end the vertical type goniometer, and the sample fixed and the vertical type goniometer. Particularly the sample horizontally fixed and the vertical type is referred to as a horizontal type goniometer.
In the conventional goniometer, any one of the X-ray source, the sample and the X-ray detector disposed adjacent the receiving slit is unrotatably fixed. Selection of the component to be unrotatably fixed is determined on the basis of intended advantages. However, each of the three unrotatably fixed manners may inherently provide disadvantages. That is, the X-ray source fixed type has a disadvantage in that a heavy weight structure is not applicable to both the sample table and the X-ray detector because of necessity of their rotation. Therefore, attachments of heavy weight, such as high pressure vessel, cannot be provided on the sample table. Further, an X-ray detector of heavy weight, such as a solid state detector, cannot be utilized. On the other hand, in the X-ray source fixed type, a large scale X-ray source cannot be used because of the necessity of its rotation.